The sea contains large amounts of dissolved material, including minerals and dissolved gases. It also contains very large numbers of organisms of all sizes.
We know a great deal about the general shape of the ocean bottoms from echo sounding, where reflected sonar signals allow the bottom to be mapped accurately.
We know about the ocean bottoms from drilling programs, from remotely controlled submarines and from instruments lowered to gather samples and data.
Cold water contains more dissolved gases than warm water, and in particular, it contains more dissolved oxygen, making it easier for aquatic animals to breathe.
The world's ocean currents are all interlinked, so that the blockage of any channel, anywhere in the world, could have major effects elsewhere in the world.
Cold ocean currents that are forced to the surface carry large amounts of mineral nutrients, and these upwellings support high levels of productivity.
Storm systems spin around a low pressure zone in accordance with the Coriolis effect, so they go clockwise in the south, counter-clockwise in the north.
Tides and waves bring about smaller scale water movements than those created by ocean currents, but even these are able to move sediment on and along beaches.
Winds and ocean currents spread life forms around the world, in large part as rafts washed down flooded rivers, which act as temporary refuges for vertebrates.
In the past, it is likely that volcanic activity near Indonesia has changed local, and thus world ocean current patterns by opening and closing various gaps.
The number of icebergs seen outside the Arctic and Antarctic Circles has increased with global warming, because this causes glaciers to lose ice faster.
In the oceans, iron is usually the limiting factor: it has been suggested that algal blooms could be generated to act as a carbon sink by adding iron salts.